Solar electric is a familiar concept, costs fall and efficiencies improve year on year. A typical cell will show an energy profit in about 2-4 years with an economic life cycle of twenty years or so and a CO2 saving of some1kilo or so for every kilowatt of energy generated, Solarex SX modules are guaranteed to maintain their charge performance over twenty years and modules of this type will probably last for many more years. Silent in operation, very reliable, no moving parts, simple to use, long lasting, modular, safe, an inexhaustable supply of energy. There are many manufacturers of Photovoltaics, two of the largest are actually owned by oil companies: B.P. and Solarex (Amoco). The most efficient modules in terms of power to surface area ratio give about 100watts for 1m2 of area with an efficiency of 14% or more (energy from available sunlight). Gains can be made by using reflective materials to bounce nearby light into a module. It is important never to cast a shadow on even a small part of a module as performance will seriously deteriorate.

Photovltaic cells are made from silicon with a tiny amount of boron added, the underside surface is positive, the upperside is then treated with phosphoric acid and is negative, when a cell is exposed to sunlight electrons in the surface are displaced, when a circuit back to the positive side is made, the free electrons flow towards it.

There are three main different types of photovoltaic cell; monocrystaline is the most efficient (upto 15%) and the most expensive to manufacture, it is a slice of crystal. Then comes polycrystaline at (about12%) made from a slice of many compacted crystals. Finally we have amorphous, which is easy to manufacture (5%) this is sprayed onto the glass in which it is contained, these cells deteriorate over 20 years or so and can also lose a lot of their charge capacity within a short space of time. Multiple thin film cells have also now been developed where many thin layers are stacked together and a type of concentrator cell whereby the light is focussed by a lens is also in existence mainly for micro modules. Another efficiency gain can be made by using a system which tracks the array to follow the sun, using a tracking switch and two small motors. Larger systems in western countries are often grid interconnected whereby excess energy is exported and defecit is imported and there are many large commercial photovoltaic facilities around the world which generate directly for the local electricity grid.